There is a frequent need to check on infusion devices as used for a variety of treatments for infusing fluids into medical patients. There are a vast number of infusion devices with the different types giving different rates of flow; the total range needed is from 1 milliliter per hour to 1 liter per hour and in special cases even values outside this range may be called for. One way of measuring flow rates is to have the infusion device pump a liquid into a container or tube and to measure the time difference for the liquid to pass between two sensors; knowing the volume between the two sensors and the time difference, it is easy to calculate the flow rate. However the infusion devices do not have a uniform flow rate due to sanction effects and it is difficult to calculate flow rates over a wide range of flow rates accurately without changing the tube or container. The present invention aims at providing a measuring device with a wide range of measurement without requiring containers or tubes to be replaced to cope with different flow rates.